The present invention relates to a controlled, externally operable brake booster, which can be activated by means of an electromagnet which is, for its part, positioned within a control circuit, the nominal value of which is preset by a superordinated control unit, as well as process for the operation of the same.
Such a type of controlled, externally operable brake booster is already known, for example, from DE 43 24 688. The electromagnet in this is seated centrally within the control casing of the brake booster. During an externally-triggered operation of the brake booster, the electromagnet is nearly permanently live. This leads to a heating of the electromagnet which becomes evident, above a certain critical range, in the form of lower power. In extreme cases, this can result in the fact that the power of the electromagnet is no longer sufficient to activate the brake booster. Since the electromagnet is positioned at a central point within the control casing of the brake booster, a sufficient cooling of the electromagnet is either not possible, or only at very high expense. The placing of an additional temperature sensor is, for reasons of space and cost, little advantageous.
It is the object of the present invention to propose measures which make a monitoring of the magnet temperature possible, without requiring an additional temperature sensory equipment for the same.
In accordance with the invention, means are provided which determine, from the nominal and/or the actual values of the control circuit, a quantity (parameter) which is proportional to the average temperature of the electromagnet. This has the advantage that no special temperature sensors are necessary. The parameter can be determined during a control process by means of the nominal or actual values of the control circuit which are present in any event and be processed.
The parameter is preferably stored in a signal processing unit and passed along to a monitoring unit. On the basis of the nominal and/or actual values of the control circuit, the signal process unit carries out a parameter estimation. The monitoring unit reports an error function to a superordinated function unit, which can then, for example, cut off the adjustment or the control, issue a warning indication, or react in a similar, predetermined manner.
It is provided, furthermore, to check the input values and/or the estimated parameters for their plausibility and to only pass along the parameters if the plausibility test turns out to be positive. If the estimated parameter is outside of a specific, theoretically possible range, or if the nominal or actual values which are processed by the signal processing unit move outside of a range in which a reasonable estimate is to be expected, then a negative plausibility testing signal is passed along to the release unit. This can either pass the last determined value which has been found to be plausible along to the monitoring unit, issue an error function report, or react in some other manner. The actual values of the current and the voltage of the electromagnet, as well as the travel of the armature of the electromagnet, are preferably processed, which guarantees a high precision of the next-following estimate, since the actual values of the current and voltage are, in particular, correlated relatively strongly with the temperature of the electromagnet.
One additional advantageous possibility consists of applying the nominal and actual values of the currents of the electromagnet for the estimate. This is possible if the electromagnet is controlled by a current control unit and makes it possible to carry out the estimate with simple means.
The parameters {circumflex over ("THgr")} for the static and dynamic behavior of the current control circuit are thereby estimated. Conclusions about the average temperature xcex8 of the electromagnet can be drawn on the basis of these parameters (static amplification factor becoming slighter, dynamics tapering off).
The nominal and/or the actual values are preferably scanned in short, equidistant intervals of time. The estimate is carried out by means of a mathematical parametric model of the electromagnet, which is deposited in the signal processing unit and makes possible a correlation between the nominal and/or the actual values and the physical parameters of the electromagnet. The parameter can thereby be either the temperature or another temperature-dependent quantity, such as a temperature-dependent resistance, for example.
The process in accordance with the invention can be used both for the operation of a controlled, externally-triggered [braking] booster as well as, in general, for the monitoring of the temperature of an electromagnet which is controlled in a position-proportional manner. It offers the advantage that nominal and/or actual values which are present in any event are used without being meshed into the control process in a disruptive manner. Defined static measuring conditions are not necessary. A parameter, an average resistance, or an average temperature can be estimated here, too, by means of a mathematically parameterized model of the electromagnet.
Further advantages of the invention proceed from the following description by means of two examples.